Pointer instruments are widely used especially in the field of medical navigation, wherein this also applies to the instruments in accordance with the invention as described here. One specific type of use is to move the tip of the pointer instrument to points on the patient (landmarks) or on medical auxiliary devices, wherein calibrated or pre-calibrated pointer instruments are localized with the aid of a medical tracking system (for example via cameras and position markers on the instrument); the position of the tip of the instrument is thus known and therefore also the position of the landmark or, in very general terms, the point to which the pointer tip is moved.
Thus, this results on the one hand in a necessity to calibrate the instrument before it is used and/or a necessity to use a pre-calibrated instrument, the shape and dimensions of which—in particular, the position of the tip—has to be known to the navigation system. On the other hand, using such an instrument with a navigation system is in most cases still very operatively intensive, because the user always has to inform the navigation system that he is currently moving to a landmark, such that its position can be recorded and/or stored. If a number of points are successively recorded or a contour profile is continuously traveled using the pointer tip, difficulties can result because the navigation system constantly has to be informed as to whether the pointer tip is currently lying on the contour to be scanned or is being lifted and transferred to another location. If navigation is not “informed” in good time in the latter case, completely meaningless contour data is recorded during the transfer movement of the pointer.